The Influence of Climate Change on Global Crop Productivity
Year: 2012
Type: review
Abstract: Climate trends over the past few decades have been fairly rapid in many agricultural regions around the world, and increases in atmospheric carbon dioxide (CO2) and ozone (O3) levels have also been ubiquitous. The virtual certainty that climate and CO2 will continue to trend in the future raises many questions related to food security, one of which is whether the aggregate productivity of global agriculture will be affected. We outline the mechanisms by which these changes affect crop yields and present estimates of past and future impacts of climate and CO2 trends. The review focuses on global scale grain productivity, notwithstanding the many other scales and outcomes of interest to food security. Over the next few decades, CO2 trends will likely increase global yields by roughly 1.8% per decade. At the same time, warming trends are likely to reduce global yields by roughly 1.5% per decade without effective adaptation, with a plausible range from roughly 0% to 4%. The upper end of this range is half of the expected 8% rate of gain from technological and management improvements over the next few decades. Many global change factors that will likely challenge yields, including higher O3 and greater rainfall intensity, are not considered in most current assessments. Many factors will shape global food security over the next few decades, including changes in rates of human population growth, income growth and distribution, dietary preferences, disease incidence, increased demand for land and water resources for other uses (i.e. bioenergy production, carbon sequestration, and urban development), and rates of improvement in agricultural productivity. This latter factor, which we define here simply as crop yield (i.e., metric tons of grain production per hectare of land), is a particular emphasis of the plant science community, as researchers and farmers seek to sustain the impressive historical gains associated with improved genetics and agronomic management of major food crops. Sources of growth in agricultural productivity are also multifaceted and include levels of funding for public and private research and development, changes in soil quality, availability and cost of mineral fertilizers, atmospheric concentrations of CO2 and ozone (O3), and changes in temperature (T) and precipitation (P) conditions. This Update focuses on changes in weather, CO2, and O3 in agricultural areas and how that has affected and will affect crop productivity. In doing so, we recognize that this is only part of the fuller story on crop productivity, which in turn is only part of the fuller story on future food security. For example, this Update is silent on the many ways that global change can influence food security via pathways other than agricultural productivity, such as by influencing human disease incidence or income growth rates. The main question of interest here is the following: how important will climate change and CO2 be in shaping future crop yields at the global scale, relative to the many other factors that influence productivity? This question helps to set the challenge of climate adaptation in context. We are less concerned, for example, with whether impacts are statistically distinguishable from zero than with whether they are costly enough to justify a major acceleration of investment in agriculture in order to reach target growth rates. Two spatial scales are of primary interest when discussing impacts of climate change on food security. One is the global scale, because most major sources of human calories (e.g. maize [Zea mays] or wheat [Triticum aestivum]) are international commodities whose prices are determined by the balance of global supply and demand. In this context, individual regions are only of interest to the extent that they contribute to global supply. However, it is equally true that not all areas are fully integrated into global markets. In fact, many of the poorest and most food-insecure areas currently lack the infrastructure and institutions needed to fully participate in global (and sometimes even regional) markets. Although most of these areas are more integrated into global markets than they used to be, and will be even more so over the next few decades, it is important that assessments of global food security consider local and regional impacts in addition to those at the global scale. If nothing else, transport costs will always make local supply more closely tied than global supply to local prices. For brevity and focus, this Update discusses mainly global-scale issues. Similarly, climate impact assessments must make choices about which crops to consider. By far, the most common crops considered in published studies to date are (in order) wheat, maize, rice (Oryza sativa), and soybean (Glycine max; White et al., 2011). These crops are the main sources of human and livestock calories globally as well as in many regions (Fig. 1A). They also directly or indirectly (via livestock) provide the bulk of protein in many regions (Fig. 1B). However, many other foods are important sources of calories (e.g. starchy roots in Africa, nonsoybean vegetable oils, and sugar) or protein (e.g. pulses and seafood), yet there is relatively little known about the response of their production to climate change. Here, we focus on the main grain crops that are most well studied but also discuss other crops where possible. Daily calorie consumption (A) and protein supply (B) from various food sources for the globe and eight regions around the world. Data source is FAO (2012). The next section describes some of the observed and projected climate changes of relevance to agriculture, which provide a foundation for understanding past and future impacts. Subsequent sections describe the various mechanisms by which climate, CO2, and O3 changes can affect crop productivity and then integrate the understanding of climate trends and response mechanisms to discuss the likely past and future impacts of climate, CO2, and O3 changes on global crop productivity. Finally, the last two sections discuss some pending issues and conclusions. Throughout the paper, we emphasize changes and impacts not only in the future but also for the recent past. The main rationale for this approach is that past trends are a reasonable starting point for what to expect in the next decades. For example, the rates of warming in most climate models are roughly linear for the 1980 to 2050 period, both at global and regional scales (Solomon et al., 2007). In the past several decades, air temperatures have been warming in most of the major cereal cropping regions around the world. As an illustration, Figure 2 shows the linear trend in growing season average maximum and minimum T (Tmax and Tmin, respectively) for 1980 to 2011, with the growing season defined based on crop calendars from Sacks et al. (2010) for the predominant crop near the station location. Average trends were roughly 0.3°C per decade for Tmax and 0.2°C per decade for Tmin. There is a larger range in trends for Tmax as compared with Tmin (Fig. 2, C and D) due to the greater impact of changes in cloudiness and radiation (associated with both natural variability and air pollution) on daytime relative to nighttime T (Lobell et al., 2007). Decadal warming trends (°C per decade) since 1980 in growing season daily Tmin (left) and Tmax (right) in major global cereal cropping regions, displayed on maps (A and B) and as histograms (C and D). T were averaged over the crop season (taken from Sacks et al., 2010), and points were selected randomly from one-half-degree grid cells having at least 10% harvested area in one of the four major cereal crops (wheat, corn, rice, soybean; based on Monfreda et al., 2008). Weather data were generated by interpolating anomalies of surface weather station data (from www.ncdc.noaa.gov) relative to climate normals in the WorldClim database (www.worldclim.org). Different symbols indicate the predominant crop for each grid cell. The trends in Figure 2 are consistent with those seen in a recent analysis of gridded T data (Lobell et al., 2011), which showed T trends from 1980 to higher than of historical variability in most cropping regions and growing around the world, with the of the in T are also associated with an increased incidence of and a incidence of et al., which affect crop production as In to historical changes in growing season have been more and not relative to natural variability (Lobell et al., 2011). The of has increased in many of the et al., of relevance to agriculture, is by changes in T affect and changes in the and of Although of soil are models can be used to historical trends in agricultural and based on changes in and other In changes are not statistically in most regions, since increases in extent and have been for Africa, and and and 2011). CO2 concentrations have been since the of the with an average rate of growth of 2 per in the et al., 2011). The global average of higher than at the of the (i.e. in 2011). average O3 concentrations have also increased from to in the to at current levels due to of ozone associated with due to air can increase concentrations to over et al., have some in which are to crops levels have to et al., also observed around the globe from to associated with air and However, since global trends in radiation have been more with in some areas (e.g. and and in (e.g. and The most of global warming in agricultural areas will continue to be T Figure shows projected changes in to average T and over a from climate from each climate are averaged crop areas in The average rates of warming are to the observed rates since 1980 of roughly 0.3°C per decade (Fig. There is on whether Tmin will or than Tmax (Lobell et al., 2007). to and to in to T and for areas by from a for each indicate for each are area with to the of each grid with agriculture based on et al., 2008). Data source for climate is Although the expected rate of warming is to the past it is also plausible that rates be higher or for or For example, global surface T both and not increase for the the a that can be by natural variability the trend and it is plausible that we trends of as as in global which to as as for major agricultural regions, because land than and of indicate changes for from to by of the in such as those in Figure from of natural variability in and the of variability that from of the climate and The of will be increased in and in such as the Africa, and the (i.e. and et al., 2007). In other regions, most models not changes in that are relative to natural even by et al., 2011). more relevance to agriculture than are changes in soil and surface which on T and of in addition to in regions without projected changes in higher T will increase and with more and an associated higher of this will to trends in soil and a higher of agricultural in many agricultural land areas in the 2011). is and where projected increases in and to or increased soil CO2 levels are to for at least the next as of roughly be to current atmospheric levels et al., 2007). rates of roughly per decade can be expected to which levels to reach around this are also projected to continue in the decades, in of future O3 concentrations and radiation levels are due to the in pathways and air as well as the of ozone with a climate 2008). This Update focuses on four primary factors that have affected and will continue to affect crop production in the an CO2, and Here, we discuss the various mechanisms by which each of these impacts crop T yields main higher T crop and crop which in most is associated with yields T impacts the rates of and grain with a (e.g. maize and have higher T for than crops (e.g. rice and but even crops in at T and the can increase or on the current T relative to warming at raises costs without for warming to an increase in the of a relative warming raises the air and the which is defined as the the and the of the has roughly in recent decades over spatial scales et al., and is projected to change in the future as to because more water per of carbon gain et al., to by their but at the cost of rates and an increase in which in turn increase impacts. T can directly plant the T distribution, such that and more and less The of and will to a of the growing season in several and For example, indicate a increase in the growing season for by compared with the et al., 2011). and are also expected to gains in the for crop growth et al., the other end of the warming increases the of the period, which can to yields, and the of crop et al., Finally, with higher atmospheric CO2, the growth and of many and to agricultural crops et al., increased incidence of agricultural will increase crop water of is a likely response in some regions, many areas lack and water can be of In with or to also be to by the In crop will to soil by their and carbon to water T and impacts. the of cereal crops be et al., 2011), changes in the of the in for farmers to Finally, more rainfall to and also pathways for crop atmospheric CO2 concentrations provide some to the impacts of T and soil higher CO2 has a in such as wheat, rice, and most and vegetable that costs in the are by higher CO2 also has the of in both and crops and are to be by in an atmospheric CO2 the relative of this studies and is a of in the et al., the that CO2 reduce the of in cropping and protein concentrations in yield et al., 2008). such as carbon and with in the of to which to in all major crop et al., from air can also reduce These impacts are likely to be in agricultural areas of urban regions, but O3 can also be In fact, O3 concentrations levels are currently in most agricultural regions of the globe et al., also O3 and For example, CO2 will reduce O3 by crop to the plant and production et al., However, is the of CO2 to reduce the impact of O3 on yields et al., related is that improvement in crops such as wheat has increased that higher are associated with increased rates and yields et al., However, a higher more of the of more recent to O3 et al., 2008). In the individual mechanisms are relatively well (e.g. at higher T or higher rates at CO2 in the various global change factors that is not currently well For example, of the the from higher improved from higher CO2 to reduce impacts of increases or rainfall of et al., et al., et al., and et al., et al., et al., as well as and et al., have been understanding the impact of global change mechanisms at However, the have not always been at regional scales for the future response of crop production to conditions. change factors will have impacts on cropping around the world, due to regional in rates of daytime and nighttime changes to the and of and to O3 and air of such as the crops and of also by and an important in shaping the impact of weather and climate change. are also likely to change these in response to climate for by crops or the of or and the to make these changes will by atmospheric CO2 which will be around the world, will have because of of crop and conditions. than a review of the observed or expected this section discusses some important in cropping that of the in impacts. are less than by higher because of warming on water and greater rates to and related to T For example, maize in the which is is less to than in and some such as rice and to be more than also a the relatively of crops to For example, rice from higher Tmax in many at least Tmax that higher Tmin is et al., crops growing in areas will to crops. Different crop have T as well as to CO2 and One is crops that in such as wheat and crops from such as and recent of the et al., season average T of for wheat, for maize, for for rice and and for and some et al. a from which we the important for CO2 is and and crops For example, a recent of showed roughly a of for a CO2 increase from to et al., but that regional or global average yield is the of crop production relative to Figure data on average growing season T and average yield for individual over the past two decades from et al. The of in the the relative to global production of the crop (e.g. has the for rice, the for of is because many factors affect yields other than However, for several there is a for yields to the which is by the based on the from et al. that is not by et al. so we the same as for wheat, since have a or T in Figure is for some most have average season T that is warming likely to the of the global production will to for Average yields for major crops average growing season T as by et al. a with the of the to production for that indicate T for yields based on as by et al. The yields are observed to the with average yields for is that many that are major are currently In with there be more to weather the lack of other factors and At the same time, will also be to of CO2 in crops and For with fertilizers, such as in many higher atmospheric CO2 to production but higher CO2 is also more likely to protein levels without into the et al., 2008). will also and in their to and for change. an understanding of observed and projected trends in climate, CO2, and O3 as well as of crop yield to these it to the impact of changes in these factors on global crop productivity. is to these than directly even when past because it is simply not to a in which climate not to impacts of climate and other it is to the of productivity growth in of most major crops have increased over the past half due to greater of and crop Figure shows average global yields for the most important crops in of calorie production as well as linear trends by decade. At the global scale, yield growth has been fairly linear over the past with the of which has not improved since this linear growth rate to a increase over (Fig. The global aggregate also a of important with many of growth rates the global story has been one of improvement in yields at a fairly rate over the last half global average yields since for major crops. rates of yield change per decade for each decade on the of the to of data yield changes per decade for each decade. Data source is FAO (2012). important point when observed trends is that they the impact of all factors influencing including changes in climate and historical trends are used simply as an for growth, but they are more as the of various the most important of which is but not growing of studies have to impacts of recent climate trends on crop Here, we present the main from a global-scale which impacts for the 1980 to (Lobell et al., 2011). trends were to have wheat and maize yields by roughly and over the period, with relatively impacts of trends. soybean and rice yields were to be relatively by changes so Figure the from et al. with for and for with and for maize, and wheat all increased since but not as as they have climate for a of climate and CO2 trend are also the of higher CO2 for crops as roughly for the increase over this yields in 1980 and on the to data for with yields for of climate trends since 1980 or climate or CO2 trends since These are based on from et al. The in Figure are by increased as changes in were at the global scale. The impact of climate, can be as the of the warming in Figure 2 and the that most wheat, and maize areas are their T (Fig. crops in Figure a larger yields in 1980 and than the observed and yields in this as that climate has a impact on global food production or food security. However, food demand has also increased since so global prices and food security continue to be to in supply. For example, the roughly in calories due to climate trends since 1980 as a average of the individual crop to to a roughly increase in prices relative to a with warming (Lobell et al., 2011). is also that by in the not consider recent that several major climate in in that on food supply and prices. studies have projected impacts of climate and CO2 changes on future crop and of these studies are et al., and point to a that the of CO2 at the global scale will be by the from climate change by CO2 and other There is about when impacts will As there is that global impacts for 1980 to were (Lobell et al., due to climate trends this historical period, that on warming than the of warming due to We present in a of how two global change factors global productivity and over the next few decades. These are as estimates of the impact on calorie supply from all major averaged over the next likely in the near is that warming will global yield growth by about 1.5% per decade CO2 increases will yields by roughly the same This balance is consistent with the global from many studies and major assessments. it is likely that CO2 will and climate will be larger et al., 2007). The most likely and plausible are both are based on of various sources et al., and et al., et al., 2011). over for for and which be and The most likely and plausible are both are based on of various sources et al., and et al., et al., 2011). over for for and which be and also the range of plausible outcomes in the near which less in the than the most likely is plausible that the of warming and CO2 be as as per decade or as as per on how T and CO2 change and how crop yields turn to consider whether is a one is rates of yield growth in recent decades, which around an average of roughly per decade (Fig. that climate and CO2 a roughly linear of recent yield in in a growth rate of roughly 8% per decade to 2050 or gains of to per decade a of past future yield important in of climate change impacts on agriculture is that the on the particular question at There are at least on global-scale productivity even without the set of questions related to or have on the question of the of in order to In that of most relevance is the of CO2 all associated climate However, one is on related to adaptation to T and the of climate change are of interest in of the of If one is in the question of how to for climate and CO2 in of productivity growth, the is how the of climate and CO2 will change from one decade to the because historical yield trends include the of past climate and CO2 trends. estimates of global change impacts on global-scale crop yield trends will several such as rates of global T increase or the of farmers in the of are the of the plant Here, we that to the of this the of of CO2 and T are not well For example, how CO2 reduce water associated with and how it increase to because of from how T reduce the of CO2 by and grain as in the the of O3 are not into most studies of global change impacts. understanding of how O3 yields by and in with T and CO2, and improved of current understanding in crop are both what are the and of changes relative to other adaptation such as of agricultural areas higher or agriculture and as a to soil are the crop changes and agronomic and what is the balance in rates in aggregate crop productivity to 2050 will continue to be mainly by technological and agronomic as they have for the past in the most it is that climate change in a in global the question at the global scale is how of a climate change present in the to productivity growing as as demand. the of climate change and CO2 on global average supply of calories is likely to be fairly to zero over the next few decades, but it be as as to of yield trends. this global many changes at scales that be of relevance to food security, even global production is et al., 2007). reduce in global estimates of rates of global warming and of crop yields to warming and CO2 (and their be We that the of yields will on the crops including improvements to reduce to T or to CO2, as well as management changes by farmers in and how to their crops. The of changes in O3 are currently less but also a impact at the global scale. will be to the of changes in climate, CO2, and the scale of global food production and the that agriculture is always in However, the science related to climate change and crop that climate change a to global productivity growth at rates to with demand. the scale of in crop and the emphasis of these on global change will to sustain yield growth over the next few decades. ozone temperature precipitation maximum temperature minimum temperature
Source: PLANT PHYSIOLOGY
Authors: David B. Lobell, Sharon M. Gourdji
Institution: Stanford University
Language: English
Subfield: Agronomy and Crop Science
Domain: Life Sciences
SDGs: Climate action, Zero hunger
Open Access status: green
OpenAlex ID: W2071452287